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Issue with my feed line.
27 August 2020 | by  |
| Troubling reading of coax |
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| Faulty PL259 |
Last week I posted about a wonky SWR reading I was getting and I figured it may be the result of a loose PL259. The issue returned again but not as bad last week. Since moving my Endfed antenna to be able to extend the wire the coax was also moved and now has to be buried. I needed to place the coax in some PVC conduit and not direct buried underground. It was a nice day and I decided to place the coax in the PVC conduit. While I had the coax disconnected from the Endfed antenna to feed it through the PCV conduit I thought I would connect my Fluke multimeter to the coax. With both ends of the coax disconnected, I placed the multimeter leads across the centre and barrel of the PL259 just to make sure my reading was "OL" and low and behold it was not!
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| Outdoor soldering station. |
As I wiggled and moved the PL259 the reading would rise and fall. Truth be told this PL259 was a plastic moulded factor installed connector that I was not too keen on but for some reason decided to leave it on. Just to confirm it was the PL259 I cut it off the coax and then retested the coax from the centre conductor to braid and the meter read "OL" Fortunately I just installed 120-volt outlets in my shed so it was a matter of running an extension cord from the shed to an outdoor soldering station I set up to solder in a new PL229 connector.
11 Responses to “Issue with my feed line.”
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Hi again Mike,
This is a problem I have seen over the years when the coax is using a solid copper center wire and not a stranded center wire. The wire will normally snap and can still make contact, but can also loose it. The other issue is a cold solder joint or crimp, but the broken wire is the most common. Glad you found the problem. Hope you are back on the air now.
73 Harry K7ZOV
I agree with Harry, but apparently this time that was not Mike’s problem 🙂 His Fluke was showing “some resistance”, so that was not the what often happens with solid inner wire.
What Harry is saying highlights the need for two types of “simple tests” – with both ends “open” check that ohm meter is showing OL, but also test that with one end shorted your meter is showing (very) small resistance.
The first test (Mike’s) will discover OBVIOUS shorts in cable, the one from Harry’s “case” will detect (most) breaks in cable.
There is a whole other side of faulty cables, but that requires testing with high voltage (DC), at least twice the voltage your TX will “cause” on the cable (can be VERY high if SWR is high!!!). This will reveal any imperfection in insulation, especially melted insulation at the point where cable enters connector!
And then RF testing – any sharp bends or pinched cable can (and will) significantly change cable’s impedance at that point, and reflect significant part of energy back.
So, you get 3 options 🙂
1) test nothing, give it a try, hope your TX can handle high SWR
2) test everything
3) do basic “due diligence” – use ohm meter to test for “short” and “open”
I do have one concern and that is when putting coax in PVC piping which is underground, I’ve read some people have found condensation forming in the PVC. This can’t be good for the coax that is inside of the PVC. Glad you found the problem though.
Good morning Harry, the coax that I am using does not use a solid centre but a stranded one. In the past the only coax I used with a solid centre was LMR 400. This issue is fixed now, and I am back on the air making contacts! Always Harry nice to hear from you, stay well and all the best.
73,
Mike
VE9KK
Good morning Miro and thanks for taking the time to leave a nice detailed comment. As for the meter reading on the Fluke it was very hard to capture the meter running up and down the ohms scale. Trying to take a picture and hold the coax and the leads on the coax was a treat. The common reading I was getting was in the mega ohms range. Unfortunately I am not able to DC hi pot the cable for insulation breakdown. Before I retired from the hydro we did that all the time on high voltage cables to check for insulation breakdown. Or we meggered the cable but again I don’t have access to a megger anymore. Thanks, Miro, for all the great info,
73,
Mike
VE9KK
Good morning Dean, thanks for taking the time to read the post and leave a comment. I have read the same as well but also have read to drill holes in the bottom of the PVC pipe for drainage. I did not do that and the pipe length is only about 8 feet to the shed. At one of my previous homes I had LMR 400 in poly pipe and the run was about 150 feet underground. I sealed each end of the pipe and it was underground for about 4 years. Before we moved to a new place I pulled the LMR 400 out of the pipe and it was dry and now issues. I am hoping this 8 foot run will cause me not issues……but if it does I will be for sure blogging about it.
Thanks for stopping by Dean and have a great weekend.
73,
Mike
Plastic UHF connector? I rather dislike them on a good day. Now with plastic ones being made it brings a whole new world of hate for them. Geez!
Good morning Joe thanks for taking the time to read the post, as for the PL259 the whole connector is not plastic it is the housing around the connector that is plastic. I don’t like it as I can’t access the connector for troubleshooting without cutting off the plastic housing around the connector.
73 and have a good weekend.
Mike
VE9KK
As a (retired now) Union Electrician I installed LOTS of underground…
If ya don’t make SURE & use LOTS of glue on the fittings it WILL leak…
I found the best way to cure that problem is to use roofing tar on the couplings. All around each joint, where the seams are.
If it is a coupling & 2 male ends, both sides. If it is a pipe with a pre formed coupling, only at the ‘joint’. If a coupling with 2 male
pieces BOTH SIDES… ‘glob’ it on, cover the seams COMPLETELY.
Rick, KI5KV (ex Assistant Business Agent IBEW 520)
…also use pvc cleaner, & light sanding w a fine grit sandpaper (automotive 400 grit) b4 cleaner…
Good morning Rick and thanks for the comment, I agree but in my case it was only one length of PVC so there was no coupling involved just had to later on seal the ends where the coax exited the pipe. When I was back in Ontario (retired now in New Brunswick) for 30 plus years I was with the Power Works Union. I have a substation Electrician ticket and construction maintenance ticket as well.
We also have the IBEW up in Ontario as well but our union was the Power workers.
73,
Mike
VE9KK